1. Field of the Invention
The present invention is directed to a method of manufacturing an automotive reflector. More specifically, the invention is directed to manufacturing an automotive reflector from a thermoformed film having a highly reflective material that is integrally molded into a reflector.
2. Description of the Related Arts
Most automotive reflector assemblies are made from a reflector and a lens. The reflector is injection molded to have a curved shape. The interior of the reflector is metalized to provide a highly reflective coating. The metalized surface is produced in several ways including vacuum deposition, sputter coatings or ion coatings. These coating methods generally require that the reflector be pre-molded and placed within a metalizing chamber. Most chambers are operated under a vacuum and require removing some or all of the air within the chamber. A significant percentage of the metal used in the metalization process falls outside of the reflector. This generally requires the use of protective masks that are fitted over the reflectors to prevent metalization of these outside areas. The method thus described is a batch process that requires loading and unloading the reflectors into a chamber for metalization.
The conventional metalization process is described in U.S. Pat. No. 4,085,248. The interior surface of the reflector requires a highly polished or smooth finish to receive the metalization. This is achieved by either finely polishing the molds or by applying a base coat to the interior surface of the reflector. The metal is deposited on the interior surface of the reflector usually by vacuum deposition. The metal most commonly used in vacuum deposition is aluminum. Because the aluminum surface is subject to oxidation, a protective outer coating is deposited atop the aluminum to maintain the reflectivity of the aluminum coating. It is desirable to produce a reflector without these metalization and coating steps.
It is also desirable to manufacture reflectors from plastic materials that withstand the high temperatures created by the lamp. Currently, most high quality thermoplastic reflectors are made from unfilled-engineered plastic materials such as polycarbonate. These materials are able to both provide the desired high temperature resistance and smooth finish for an optical surface, but they are more expensive than other plastic materials. Plastic materials filled with reinforcing fibers or particles are also known to be able to withstand the higher temperatures, and cost substantially less than the unfilled polycarbonate, but the filler material, usually glass, talc, or mica, causes surface irregularities that degrade the optical performance of the reflector. These materials require a base coat between the plastic reflector and the metalized coating to provide a smooth surface. This additional step may negate the cost savings from the materials selection.
It is also desirable to separate the metalization step from the molding step. The metalization chambers required to produce an optical-quality surface are very expensive. The equipment needed to injection mold the reflector is much more affordable. Rather than shipping bulky metalized reflectors to assembly facilities, it is desirable to manufacture a lightweight pre-form that contains the metalized coating reflective surface. This enables the manufacture of the finished reflector at the final assembly location and permits the greater utilization of the more expensive metalization chambers.
U.S. Pat. No. 5,833,889, teaches a method of making an automotive reflector by first thermoforming a polymeric film to have the shape of the reflector and then injection molding a rigid backing to the film. The backing may include glass reinforcement material that in the absence of the film would degrade the optical coating. The film provides a smooth surface to receive the metalization. The method described in the U.S. Pat. No. 5,822,899 patent still requires a separate metalization step that is avoided by the present process. By incorporating the reflective material into the film prior to forming, the expensive and complicated metalization process is avoided. It is much simpler and less costly to form a flat film to have a reflective surface than applying metal to a curved reflector.
In an unrelated art area, it is known to apply decorative films or appliquxc3xa9s to the exterior surface of molded articles. U.S. Pat. Nos. 5,266,377 and 5,223,315 teach the manufacture of a container having a printed label. The label is placed within the cavity of the mold and then the container is molded within the label. Applying films to the exterior surface of an article is understood because as the article is formed within the mold, it pushes outwardly, stretching the film within the mold. It is not known to manufacture articles having a smooth film surface laminated to the surface of the part. Manufacturing an article having a smooth laminated interior film is more complex because as the article is molded, it tends to collapse the film within the mold. The collapsed film often causes wrinkles, pleats or other unwanted blemishes.
The films used to produce thermoformed pre-forms are generally placed within a rigid frame. The frame retains two or more sides of the film while the film is heated. The film and frame are then placed above or below the mold for thermoforming. A process using frames to thermoform films is described in UK Patent Application No. 6B2187132A and is incorporated herein by reference. The use of frames is again a batch process where the frame receives a length of film. The frame is needed to provide tension to the film as it is thermoformed. It is desirable to provide a method for manufacturing thermoformed films that does not require the use of a frame to retain the film or to provide tension to the film during thermoforming. It is also desirable to provide a method of precisely indexing the film without the need for a frame.
After the film is thermoformed, it produces a pre-form having an offal portion surrounding the pre-form. The offal portion is trimmed in a separate trimming operation and removed from the pre-form. It is desirable to provide a thermoforming process that simultaneously thermoforms and trims the pre-form while retaining the offal portion on a film roll. This enables a continuous thermoforming and trimming process that does not require the separate handling of the offal portion.
These deficiencies and problems are overcome by the present invention.
The present invention is directed to a method of manufacturing an automotive reflector comprising a series of steps. A thin plastic film having a backing material is thermoformed into the rough shape of the reflector. The thermoformed film is called a pre-form. The pre-form has a concave surface and a convex surface. The backing material forms the convex surface. It is preferable that the film be formed to have a highly reflective surface. This may be achieved by depositing a metal coating to the film using conventional metalization equipment or by incorporating material, either polymeric or metallic, into the film that produces a reflective surface on the film.
The pre-form is placed within an injection molding press with the concave reflector surface juxtaposed a mold core. Molten plastic material is injected into the mold adjacent to the backing material. The plastic material heats and fuses to the backing material to form a reflector. After the plastic material has cooled, the reflector is removed from the injection mold as a finished reflector.
In an alternative embodiment of the present invention, the thermoforming operation may simultaneously form and trim the film. This is especially useful when using films that have a reflective surface and the offal portion is not needed as a mask. In this alternative embodiment, the film is retailed between rollers and thermoformed in the desired shape. The thermoforming press includes cutting blades that trim the film to the desired shape when the mold is moved to a closed position.
This alternative embodiment enables the manufacture of a reflector without the need for a separate metalization step. The film has a highly reflective material that provides the reflectivity necessary for automotive reflectors. It is thermoformed into the rough shape of the finished reflector and integrally molded with plastic material in a process described as insert molding.
Utilizing a coiled film stock further enhances the manufacturing method. The film stock is indexed using a sprocketed roller. The film is thermoformed into a pre-form while the sprockets retain the film perimeter. The thermoforming step simultaneously forms the film into a pre-form and trims and or severs the perimeter of the pre-form from the remainder of the film. The pre-form is removed from the film leaving blanks. The film surrounding the blanks constitutes the offal portion of the film and is taken up by a take-up spool.
The process eliminates the need for a frame to retain the film. The process also eliminates separately collecting the offal portion from the trimmed pre-form.
These and other objects, features, and advantages of the present invention will become more readily apparent when viewed in connection with the accompanying drawings wherein like reference numbers correspond to like components.